Such devices and methods employ vapor deposition, gas diffusion, plasma spraying, or deposition by sputtering in a respective apparatus. One type of such apparatus comprises a rotatable platform carrying in turn rotatable disks on which sets of structural components or individual components are positioned for the coating operation. The rotatable disks on the platform make sure that a uniform coating is achieved for sets of components or for each individual component. The rotatable platform in turn makes sure that the set of components or the individual components can be transported into different stations of the coating apparatus. A disadvantage of the just described apparatus is seen in that where a partial coating is intended, it is necessary to mask the component surfaces that are not to be coated. The application of such masking either by cover screens or by protective coatings is very cost intensive since manual labor is involved.
Yet another disadvantage of the known devices and methods is seen in that the consumption of coating material is rather high because the masking and any other covers and the large surface areas of the walls of the coating chamber are also coated. As a result, any attempt to recover coating material involves a high technical effort and expense, especially with regard to the large surface areas of the chamber and of the maskings which are coated only with very thin coating layers. Such thin layers are difficult to recover.
The above difficulties encountered with conventional coating devices and methods are especially disadvantageous where propulsion plant blades, such as turbine blades are to be coated with precious metals. Due to strength considerations, blades for a rotor disk may not be coated on the foot surfaces nor on the radially inwardly facing platform surface which merges directly into the foot area. Moreover, the cross-section of the blade foot has a complex, multi-dovetailing cross-sectional configuration which can be effectively protected against coating only with respectively complex masks, the production and application of which are expensive. Moreover, if propulsion plant blades are equipped with shroud band segments, it also becomes necessary due to strength and fit considerations to apply the coating only partially on those surface areas that are exposed to gases in the flow channel of the engine or propulsion plant. In addition to the substantial quantity of coating material that is deposited with loss on the masking surfaces, stray losses occur due to the coating of surfaces of the coating apparatus.